1. Do not have "oil mark". Observe whether the packaging is complete, whether there is leakage, cans, caps are rusty, abrasions, whether the trademark immersion oil.
2. Do not buy "fat to listen to." Watch the bottom of the tank, cans or caps. Cans, caps slightly concave, if found cans, caps raised outward do not buy.
3. sound crisp bright. Hand hit the lid, the sound crisp when the quality; and voiced note has been bad.
4. Trademarks should be complete. Observe the production date and shelf life of the product, the trademark is not complete or near the shelf life of the product to be careful to buy.